The long term aims are 1) to describe the normal functional anatomy of the jaw muscles by EMG recordings and analyze how dysfunctional muscle activity in the head and neck areas may be diagnosed with electromyographic (EMG) techniques and corrected using biofeedback training, occlusal and bite splint therapy. The specific aims are to describe the normal functional anatomy of the digastric and pterygoid muscles by recording normative values for motor unit action potentials (MUPs) and their recruitment patterns during various jaw movements and swallowing, and to develop algorithms which can be used in a computer-aided system for semi-automatic detection and pattern recognition of MUPs in EMG recordings. The hypothesis is that modifications of the recruitment order of motor units are possible and occur in the digastric and pterygoid muscles when those muscles are called on to act in various ways due to differences in the tasks performed, but that these differences in activity patterns are masked when quantifying the EMG by integration. Recordings of MUP characteristics and activity patterns will be made with intramuscular electrodes, in a group of six healthy subjects with normal dentitions, from the digastric and the pterygoid muscles during jaw movements, clenching and swallowing. The signals will be amplified, filtered and digitized with high sampling rates, 25-100 KHz, and analyzed with pattern recognition programs written in C and ASYST developed for semi-automatic analysis of EMG recordings. The digastric and pterygoid muscles are multifunctional having more complex activity patterns than unifunctional muscles. The results are expected to increase the knowledge about their complicated functional anatomy and their roles in functionally related diseases in the masticatory apparatus.